1. Field of the Invention
The invention relates to a method of cleaning the inside of a milk tank, including the stages of rinsing the tank with cold water and subsequently washing the tank with a warm aqueous liquid containing a cleaning agent.
The invention also relates to a dairy farm milk storage facility including a tank and a cleaning system. The cleaning system includes a water supply structure communicating with the tank for supplying warm and cold water to the tank, a dispensing device communicating with the water supply structure for admixing a cleaning agent to the water and a control unit operatively connected to the water supply structure and to the dispensing device for controlling the water supply structure and the dispensing device. The control unit is programmed for conducting a cleaning program including the stages of rinsing the tank with cold water and subsequently washing the tank with a liquid including hot water and a cleaning agent.
2. Description of the Prior Art
Such a method and such a storage facility are disclosed in French patent application 2 446 686. The method according to this document is intended for automatically cleaning tanks for storing food products such as milk. The cleaning is carried out in the form of a three-stage cleaning cycle which includes the earlier mentioned two stages of rinsing and washing and a third stage of rinsing. During the washing stage generally up to 40 liters of lukewarm water previously gathered in a buffer reservoir are pumped into the storage tank and recirculated for a predetermined period of time.
Milk storage tanks are typically made of stainless steel, thermally insulated and maintained at a temperature of about 4.degree. C. for storing the milk at that temperature. Even after the rinsing of the tank, the tank is therefore still very cold. One disadvantage of the known system is that a large volume of the lukewarm washing mixture is required to obtain an effective washing water temperature of at least 40.degree. C. during the washing stage. This entails a correspondingly high consumption of water and also of cleaning agent which has to be admixed in a predetermined proportion.
Moreover, the instantaneous introduction of large amounts of warm washing water into the tank, leads to substantial thermal stress in the tank every day or every other day when the tank is cleaned after having been emptied and is detrimental to the cooling system. The more the washing water is heated before introduction into the cold tank, the larger are the thermal stresses caused in the tank. This in turn may lead to the formation of cracks in the tank. Such cracks may occur directly or, due to fatigue, after some time. Cracks in the walls of the tank have a detrimental effect upon the hygienic conditions in the tank, because cleaning the inside of such cracks is virtually impossible.
In some systems known from practice, it is known to rinse the tank with lukewarm water instead of with cold water. In such systems the temperature of the rinsing water is lower than the temperature of the washing water to avoid coagulation of milk residues, and in particular proteins, which have been left behind as the stored milk was discharged from the milk tank. Coagulation of milk residues causes the milk residues to clog up and to adhere to the walls of the tank more strongly, which makes it more difficult to remove these residues from the milk tank. Nevertheless, dependent on the temperature of the washing water, some coagulation has been observed and the extent to which the tank is found to be pre-warmed is only limited.
In French patent application 2 459 084 a tank cleaning system is disclosed which allows to carry out a heating phase by successive and progressive injections of small quantities of warm water to progressively preheat the tank to be cleaned. A pressure sensor is arranged in the buffer reservoir to dose the quantities of water introduced into the buffer reservoir.
Such a heating phase increases the duration and the complexity of the cleaning program. Therefore the down-time of the milk storage facility each time after the stored milk has been collected by the milk truck is prolonged. Furthermore, this system is complicated because special dosing means in the form of a pressure sensor are provided for dosing the predetermined small quantities of warm water.